[mwebb]

operating temperature
UN boosted engines .
typical "normal" at sea level vacuum values are ;

21 to 21" at hot idle ,no load, the needle must be steady smooth , flutter is NOT allowed

no load, at 2k rpm 2" more than at idle what ever the idle value is
UNless the EGR is opening like on some subaru

WOT snap values should be 0" when the throttle is opened wide and then as the engine decelerates about 24 to 25" , no load .

WOT snap means ;
as quickly as you are able ...
snap the throttle to MAX opening and the millisecond it is open , let the return spring snap it closed , DO NOT DO this in gear .

flutter at hot idle with no load =
valve train problem

no load low vacuum at hot idle almost always =
incorrect camshaft timing

no load , low vacuum at 2k rpm hot usually means restricted exhaust
...............................
these are typical values ;
there are exceptions ;
they do not apply to some engines , like 2.0 9A VW dohc engines
values will be lower at high altitude